Process for production of stainless steel thin strip and sheet having superior surface gloss and high rusting resistance

ABSTRACT

According to the present invention, a stainless steel thin strip and sheet having a superior surface gloss and high rusting resistance is produced by heating a continuous cast slab of ferritic or martensitic stainless steel containing 10 to 35% by weight of Cr at a temperature of 1100° to 1300° C. selected according to the Cr content in a combustion atmosphere having an oxygen concentration lower than 7% while adjusting the furnace staying time from preheating to extrusion to within 260 minutes, carrying out hot rolling while adjusting the rolling-finish temperature to a level higher than 900° C., carrying out mechanical descaling by adding a grinding and descaling agent, such as iron sand, having a maximum particle size smaller than 400 μm, to high-pressure water and spraying the mixture onto the steel strip, pickling the steel strip, cold-rolling the steel strip while maintaining the relationship between the roll diameter and the reduction ratio within the &#34;overlap&#34;-free region shown in FIG. 3, carrying out finish cold rolling by work rolls having a diameter smaller than 100 mm, if necessary, and subjecting the steel strip to final annealing. Optionally, a winding step may be performed after hot rolling, and/or a final pickling step may be performed after the final annealing.

TECHNICAL FIELD

The present invention relates to a process for the production offerritic stainless steel or martensitic stainless steel thin strips andsheets. More particularly, the present invention relates to a processfor producing stainless steel sheets having a good surface gloss andhigh rusting resistance or superior grindability by controlling rustingorigins. Especially, the present invention relates to slab heatingconditions and hot rolling conditions, and methods of mechanicaldescaling and cold rolling.

BACKGROUND ART

As the stainless steel thin sheet products, there can be mentioned the2B product, BA product and polished product specified by JIS. Thecommercial values of these stainless steel sheet products are determinedby surface characteristics such as the gloss, rusting resistance,presence or absence or degree of flaws called "gold dust", peculiar toBA products, and the grindability, and accordingly, there is a need toimprove these characteristics.

To satisfy this demand, there have heretofore been adopted a process inwhich a hot-rolled strip before cold rolling is annealed and pickled andthe surfaces then ground to remove flaws (called "coil grinding"), adouble rolling/annealing method, and a method in which heat streaks areformed at the cold-rolling step, but satisfactory results cannot bealways obtained according to these methods.

The inventors carried out research with a view to developing aproduction process for obtaining stainless steel thin sheets havingsuperior surface characteristics and clarified the causes of the formingof concavities and convexities on the surface of the product undervarious conditions, including slab-heating conditions and hot-rollingconditions, while omitting the coil grinding step of removing surfaceflaws by grinding the surfaces of a strip and searched for a means ofeliminating these causes.

The technical problem concerning the surface characteristics of astainless steel product is how to produce a product having a good gloss,high rusting resistance and superior grindability, and free of flawcalled "gold dust". Our research found that the main causes of thedegrading of these characteristics are "overlap" defects present on thesurface of a cold-rolled material.

These "overlap" defects are caused by the following surface unevennessesor pitting before cold-rolling.

i) A concavity formed by intergranular corrosion caused at the picklingof a hot-rolled strip.

ii) An undulation present on the surface of a pickled material, which isgenerally called "surface roughness". iii) A grind grain left at thegrinding of the surfaces of a pickled material.

Of these surface unevennesses or pitting, the concavity i) byintergranular corrosion can be prevented by the method of preventing thesensitization of the material or by the selection of appropriatecomposition for the pickling solution. In connection with the grindgrain iii) left after the grinding, desirably the grind grain is madefiner, but to prevent a formation of this unevenness, the coil grindingstep should be omitted so that no grind grain is present.

The surface unevenness ii) called "surface roughness" has a largeinfluence, because a large surface roughness results in a degradation ofthe surface properties of the product. As the means for reducing thesurface roughness of the pickled material, there have been known amethod in which the hardness of the material is increased at themechanical descaling of the material (Japanese Examined PatentPublication No. 60-56768) and a method in which the surface roughness isreduced at the pickling step, as disclosed in Japanese Examined PatentPublication No. 61-38270 and Japanese Examined Patent Publication No.49-16698.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a production process inwhich stainless steel sheet products having surface characteristics canbe obtained even if the coil grinding step is omitted, and anotherobject of the present invention is to provide a process in which astainless steel strip can be manufactured at a greatly increasedproductivity.

According to the present invention, the foregoing objects can beattained by providing a process for the production of stainless steelstrips, which comprises heating a continuously cast slab or partiallyprocessed slab of ferritic or martensitic stainless steel containing 10to 35% by weight of Cr at a temperature of 1100° to 1300° C. selectedaccording to the Cr content in combustion atmosphere having an oxygenconcentration lower than 7% while adjusting the furnace staying timefrom preheating to extraction to within 260 minutes, carrying out hotrolling while adjusting the rolling-finish finish temperature to a levelhigher than 900° C., carrying out mechanical descaling by adding agrinding and descaling agent, such as an iron sand having a maximumparticle size smaller than 400 μm, to high-pressure water and sprayingthe mixture onto the steel strip, pickling the steel strip, withoutgrinding (coil grinding) the surface of the strip, cold-rolling thesteel strip while maintaining the relationship between the roll diameterand the reduction ratio within the "overlap"-free region shown in FIG.3, and subjecting the steel strip to final annealing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the relationship between the furnace staying time atthe step of heating a stainless steel slab and the concavity depth ofthe surface of the pickled material;

FIG. 2 illustrates the relationship between the kind of descaling methodand the surface roughness of the pickled material; and

FIG. 3 shows the "overlap"-generating range relative to the combinationof the work roll diameter and the reduction ratio at the cold-rollingstep.

BEST MODE OF CARRYING OUT THE INVENTION

The history of the development of the present invention will now bedescribed.

To clarify the cause of the formation of unevennesses on the surface ofa stainless steel strip, we investigated various conditions, beginningwith a continuously cast slab. More specifically, the slab was heated ina heating furnace under various heating time and temperature conditions.Heated slabs differing in the thickness of the surface scale (oxidefilm) were hot-rolled. With respect to the hot-rolled materials, therelationship between the surface properties and the scale and the degreeof surface unevenness were examined and analyzed, and as a result, itwas found that the fundamental cause of a formation of unevenness on thesurface of the hot-rolled strip, that is, the surface roughness, is astuffing of scale, which is formed on the slab surface during theheating of the slab, into the material during the hot rolling. It alsowas found that, especially if the furnace staying time is long, aninterior oxide layer extending concavely from the scale-base materialinterface toward the base material is formed, and this concave scale iseasily stuffed into the material.

Thus, the properties of the scale and the hot rolling conditions have aclose relationship to the formation of unevennesses on the surface ofthe material. We analyzed heating conditions and hot rolling conditionsin practical lines and the depths of unevennesses on the surface of thepickled material, and as a result, found that a relationship shown inFIG. 1 is established between the slab-heating time and the depths ofunevennesses of the pickled material. As apparent from FIG. 1, thefurnace staying time at the slab-heating step has great influence on thedepths of unevennesses of the pickled material.

The unevennesses on the surface of the material in FIG. 1 were evaluatedby observing twenty optional visual fields on the surface of the pickledmaterial by an optical microscope and calculating an average value ofthe depth of four of the deepest concavities in these twenty visualfields.

Among the hot rolling conditions, the rolling temperature has theclosest relationship to the unevennesses on the surface of the pickledmaterial.

The lower the hot rolling finish temperature, the larger the unevennesson the surface of the pickled material. If the material is subjected todescaling using high-pressure water during the hot rolling, theunevenness is reduced.

Also the mechanical descaling method at the descaling step is a majorcause of an increase of the unevennesses on the surface of the pickledmaterial. According to the known shot blast method, as shown in FIG. 2if the spraying force is increased, because of increased but the surfaceconditions of the pickled material are apparently degraded. According tothe method of spraying high-pressure water in which grinding anddescaling agents, such as iron sand, is incorporated, even if thepressure of the high-pressure water is increased to 100 to 300 kg/cm²,the surface conditions of the pickled material are not degraded when theparticle size of the grinding and descaling agent such as iron sand isappropriately selected. Namely, if the particle size of the grinding anddescaling agent such as iron sand is selected so that the maximumparticle size is smaller than 400 μm, the scale can be removed withoutdegradation of the surface conditions of the material.

As pointed out hereinbefore, the causes of the formation of unevennesseson the surface of the material reside in a formation of scales at theslab-heating step, a stuffing of scales into the base material at thehot-rolling step, and the mechanical descaling method. Of course, toobtain a final product having superior surface properties, it isnecessary to eliminate these causes. We further made investigations witha view to developing a method adopted at the cold-rolling step forimproving the surface properties by repairing unevennesses on thesurface of the material.

We noted the effect of the diameter of the work roll adopted at thecold-rolling step. When work rolls having large diameter are used at thecold-rolling step, a compressive stress acts on the surface of thematerial, and if rolls having a small diameter are used, shearing stressacts on the surface of the material. Accordingly, at the cold rollingusing work rolls having a large diameter, the depth of the unevennesseson the surface of the material is gradually decreased by the compressivestress, and little "overlap" occurs. On the small diameter, theunevennesses on the surface of the material are stuffed under theshearing stress, to cause "overlap", while the surface gloss isincreased. We examined the influences of the diameter of the work rollsat the cold-rolling step and the reduction ratio on "overlap" in therolled material by using a material which was improved so as to reduceunevennesses on the surface of the material after pickling. The resultsare shown in FIG. 3.

If the cold rolling is carried out by using work rolls having a largediameter of 400 mm, even when the reduction ratio is as high as at least95%, "overlap" does not occur. On the other hand, where the cold rollingis carried out by using work rolls having a small diameter of 70 mm,"overlap" occurs at a 40% reduction ratio, and where the cold rolling iscarried out by using mark rolls having a medium diameter of 150 mm, asmall "overlap" appears if the reduction ratio is 80%.

Use of work rolls having a large diameter of, for example, 400 mm, iseffective for preventing an occurrence of "overlap", but the coldrolling using work rolls having a small diameter is effective forimproving the surface gloss. Accordingly, to obtain a final producthaving a good surface gloss without "overlap", there is preferablyadopted a method in which, at the former stage, the cold rolling iscarried out by using work rolls having a large or medium diameter in the"overlap"-free range of the combination of the work roll diameter andthe reduction ratio, to reduce the depth of unevennesses on the surfaceof the material, and at the final stage, the rolling is carried out byusing small-diameter work rolls to improve the gloss. Accordingly, it isimportant that, in the "overlap"-free range of the combination of thework roll diameter and the reduction ratio shown in FIG. 3, the coldrolling should be first carried out by using work rolls having a largediameter at the cold rolling of a pickled material. After the depth ofunevennesses on the surface of the material is reduced at the formerstage of the cold rolling by using work rolls having a large diameter,if the cold rolling is carried out at the final stage even by using workrolls having a small diameter such as 70 mm, since the unevennesses onthe surface of the material have been repaired, "overlap" does not occurand the gloss is improved.

The best mode of carrying out the present invention will now bedescribed.

As the steel used in the present invention, there can be mentionedmartensitic steels such as 13Cr steel of the AISI 410 series andferritic steels such as 17Cr steel of the AISI 430 series, and 19Crsteel having an increased Cr content.

From the viewpoint of the scale resistance of the steel at a Cr contentof 10 to 35% in the slab, the slab-heating temperature is selected fromthe range of 1100° to 1300° C. In the case of a steel having a low Crcontent of about 10%, a lower temperature of about 1100° to about 1200°C. is selected, and in the case of a steel having a Cr content of 20 to35%, a higher temperature of 1150 to 1300° C. is selected. If theslab-heating temperature is lower than 1100° C., the heating isinsufficient. If the slab-heating temperature is higher than 1300° C.,oxidation of the slab is conspicuously advanced and the grain sizebecomes coarse.

The oxygen concentration in the combustion atmosphere in the heatingfurnace should be about 5% when heating a stainless steel. If the oxygenconcenreduced.

The furnace staying time of the slab increases the unevennesses on thesurface of the hot-rolled material through the increased thickness ofthe interior scale of the slab. As pointed out hereinbefore, if thefurnace staying time is longer than 260 minutes, the degree of theunevennesses on the surface of the material is conspicuously increased.The higher the reduction ratio and the lower the material temperature atthe hot rolling, the higher the degree of the unevennesses on thesurface of the material. If the rolling-finish temperature is lower than900° C., the degree of the unevennesses is especially increased. Thehigher rolling-finish temperature is preferable, but the upper limit isdetermined by the capacity of the rolling mill and is about 1050° C.

At the step of descaling the hot-rolled steel strip to reduce theunevennesses on the surface of the material, it is necessary to adopt amechanical descaling method in which a grinding and descaling agent suchas iron sand is added to high-pressure water and the mixture is jettedonto the surface of the strip. If the maximum particle size of thegrinding and descaling agent such as iron sand is adjusted to less than400 μm, the surface conditions of the material are especially improved.After the pickling, the cold rolling is subsequently carried out withoutperforming the coil grinding of the surface of the strip.

At the cold-rolling step, the "overlap"-free range of the combination ofthe diameter of the work rolls and the reduction ratio is selected asdescribed hereinbefore, and at the former stage, the depth of theunevennesses on the surface of the material is reduced by carrying outthe rolling by using work rolls having a large diameter and at thelatter stage, the rolling is carried out by using work rolls having asmall diameter, to improve the surface gloss. At this step, the diameterof the work roll is important.

When the rolling is carried out by using work rolls having a smalldiameter, the unevennesses on the surface of the material can bepromptly repaired, but the unevennesses are drawn and yielded to cause"overlap", resulting in a degradation of the surface characteristics.

On the other hand, if the rolling is carried out by using work rollshaving a large diameter, "overlap" does not occur but the repair of theunevennesses on the surface of the material is not promptlyaccomplished. Accordingly, to prevent the occurrence of "overlap", the"overlap"-free range of the combination of the diameter of the work rolland the reduction ratio, shown in FIG. 3, should be selected. To obtaina product having an excellent surface gloss without "overlap", there ispreferably adopted a method in which unevennesses on the surface of thematerial are repaired by carrying out the rolling within the"overlap"-free range of the reduction ratio shown in FIG. 3, by usingwork rolls having a diameter of 150 to 600 mm, preferably about 400 mm,and the rolling then carried out by using work rolls having a smalldiameter of up to 100 mm, to improve the surface gloss.

In addition, the unevennesses on the surface of the material can beespecially effectively reduced by carrying out the descaling byhigh-pressure water on the inlet side of a line of finish rolling millsat the hot-rolling step.

Furthermore, if the strip is wound at a temperature higher than 600° C.after the hot rolling, to effect self-annealing, the step of annealingthe hot-rolled sheet can be omitted.

We omitted the step of annealing the hot-rolled strip in the case ofsteels having a Cr content of 10 to 18%, but the continuous annealingwas conducted in the case of the 19%Cr steel.

The surface properties of the product are not substantially influencedby the presence or absence of the step of annealing the hot-rolledsheet.

A predetermined final annealing is carried out after the cold rolling,and then pickling or bright annealing is carried out, and thereafter,temper rolling is carried out according to customary procedures.

EXAMPLE

As shown in Table 1 and 2, 13%Cr steel (SUS 410 steel), 17%Cr steel (SUS430 steel) and 19%Cr high-grade stainless steel melted and refinedaccording to customary procedures were continuously cast, and surfacesof the obtained slabs were partially processed. The SUS 410 and SUS 430steels were heated at 1180° C. in a combustion atmosphere. At this step,the slabs were heated while changing the furnace staying timecorresponding to the sum of the preheating time, heating time, andsoaking time within and outside the range of the present invention. Inthe case of the 19%Cr steel, the heating temperature was set at 1240° C.

After heating, each slab was hot-rolled to a thickness of 3 or 4 mm by ahot strip mill, and the hot strip was cooled and wound at a temperatureof 600° to 900° C.

In most runs, the hot rolling-finish temperature was adjusted to a levelhigher than 900° C., but in some runs this temperature was adjusted to alevel lower than 900° C. Moreover, in some runs, descaling byhigh-pressure water was carried out between the rough hot rolling stepand the finish hot rolling step.

Then, in the case of the 13%Cr and 17%Cr materials, the annealing of thehot-rolled sheet was omitted, but the 19%Cr material was subjected to acontinuous annealing. Then, mechanical descaling was carried out byapplying high-pressure water maintained under a pressure of 100 to 150kg/cm², in which iron sand having a maximum particle size smaller than400 μm was incorporated as the grinding and descaling agent, to thesurface of the strip. The particle size distribution of the iron sandwas controlled so that the maximum particle size was smaller than 400μm, but in some runs, iron sand having a maximum particle size largerthan 400 mm was used. Moreover, the shot blast mechanical descaling wascarried out in some runs.

Then, pickling with sulfuric acid as the pickling solution was carriedout to complete the descaling.

The surface of the obtained pickled material was examined by an opticalmicroscope, and the depth of unevennesses or pitting was measuredaccording to the method in which twenty optional visual fields wereexamined by the optical microscope, the depths of the deepestunevennesses or pitting in each visual field were measured, and theaverage value of four largest values among the collected data wascalculated.

From the results, it was found that the influences of the furnacestaying time at the slab-heating step are prominent, and if the furnacestaying time exceeds 260 minutes, the depth of unevennesses on thesurface of the material is dramatically increased. In the materialsubjected to the shot blast descaling, the unevennesses on the surfaceof the material were deep.

Then, each material was cold-rolled. At the cold-rolling step, therolling of the former stage was carried out by a tandem mill using workrolls having a diameter of 400 mm or a reverse mill using work rollshaving a diameter of 150 mm, and the finish rolling was carried out by areverse mill using work rolls having a diameter of 70 mm. In most runs,the material having a thickness of 3 or 4 mm was reduced to 1 mm at ahigh speed at the former stage by the tandem mill using work rollshaving a diameter of 400 mm. Then, the finish rolling was carried out toa thickness of 0.4 mm by a Senzimer mill having work rolls with adiameter of 70 mm.

In the case of the run of the conventional method (the steel compositionwas the same as that of SUS 430 used in the present invention), thematerial having a thickness of 3 mm was rolled to 0.4 mm by using a 70mm.

In the CG-effected run, a steel having the same composition as that ofthe 19%Cr steel used in the present invention was pickled and thensubjected to coil grinding, and the rolling was carried out in the samemanner as in the conventional method.

As a result, it was found that, in comparative runs 6, 8 and 12 and theconventional method, "overlap" was conspicuous and many defects called"gold dust" appeared, and the gloss or rusting resistance was poor.

In contrast, if the cold rolling of the former stage was carried out byusing work rolls having a large diameter (400 mm) or a medium diameter(150 mm), most of the obtained products were satisfactory. Namely, evenif unevennesses were formed on the surface of the material, therepairing action was exerted, but if the depths of the unevennesses onthe surface of the material was too large, the products were notsatisfactory.

Accordingly, it was confirmed that, by adopting process in whichunevennesses on the surface of the material are already reduced at theslab-heating step and at the former stage of the cold rolling, therolling is carried out by using work rolls having a large or mediumdiameter, a product having superior surface properties can be obtained.

                                      TABLE 1                                     __________________________________________________________________________    Composition (% by weight)                                                     Kind of Steel                                                                        C  Si Mn P  S  Cr Al Nb Ti N                                           __________________________________________________________________________    410    0.05                                                                             0.52                                                                             0.45                                                                             0.020                                                                            0.003                                                                            13.2                                                                             0.01                                                                             -- -- 0.012                                       430    0.04                                                                             0.44                                                                             0.35                                                                             0.024                                                                            0.004                                                                            16.4                                                                             0.12                                                                             -- -- 0.011                                       19Cr   0.01                                                                             0.33                                                                             0.36                                                                             0.020                                                                            0.003                                                                            19.3                                                                             0.04                                                                             0.20                                                                             0.15                                                                             0.010                                       __________________________________________________________________________

    TABLE 2          Combination** of Cold  Heating Furnace Conditions Hot Rolling     Conditions  Average Rolling Conditions Evaluation of Surface  Kind     heating furnace hot rolling- high-pressure  Depth* (μm) of large-     medium- small- of BA Product Run of temperature staying time final     descaling during Mechanical Unevennesses on diameter diameter diameter     gold  rusting No. Steel (°C.) (minutes) temperature (°C.)     hot rolling Descaling Method Pickled Sheet roll (400φ) roll (150φ     ) roll (70φ) dust gloss resistance***       (1) SUS410 1180 190 930 not effected high-pressure 10.5  75% →     60% ∘ ∘ ∘  water + iron  sand (2)     SUS430 1180 200 930 " high-pressure 11.0 67  60% ∘ .smallcirc     le. ∘  water + iron  sand (3) SUS430 1180 200 930 effected     high-pressure 9.3 67  60% ∘  ∘∘     water + iron  sand 4 SUS430 1180 200  880  not effected high-pressure     15.9 67  60% Δ∘∘  water + iron  sand (5)     SUS430 1180 240 930 " high-pressure 13.6  75% 60% ∘.smallcirc     le.∘  water + iron  sand 6 SUS430 1180  280       930 " high-pressure 18.4  75  60% x x x  water + iron  sand 7 SUS430     1180 230 930 " iron sand  15.6 75  " Δ Δ Δ (maximum     particle size larger than  400 μm) 8 SUS430 1180 230 930 " shot blast      19.4 75  60% x x x           Combination** of Cold  Heating Furnace Conditions Hot Rolling     Conditions  Average Rolling Conditions Evaluation of Surface  Kind     heating furnace hot rolling- high-pressure  Depth* (μm) of large-     medium- small- of BA Product Run of temperature  staying time finish     descaling during Mechanical Unevennesses on diameter diameter diameter     gold  rusting No. Steel (°C.) (minutes) temperature (°C.)     hot rolling Descaling Method Pickled Sheet roll (400φ) roll (150φ     ) roll (70φ) dust gloss resistance***       (9) 19Cr 1240 180 950 not effected high-pressure 6.0 67  60% .smallcirc     le.∘∘  steel  water + iron  sand (10)  19Cr 1240     230 950 effected high-pressure 9.3 67  60% ∘∘.sma     llcircle.  steel  water + iron  sand (11)  19Cr 1240 240 950 not     effected high-pressure 15.0 67  60% ∘∘.smallcircl     e.  steel water + iron  sand 12  19Cr 1240 230 950 " shot blast  16.3 67     60% x Δ Δ  steel conven- SUS430 1180 270 910 not effected     high-pressure 11.8   70  x x x tional  water + iron method  sand CG ef-     19Cr 1240 240 920 " high-pressure 10.0  70  Δ Δ Δ     fected  water +     Note     Runs (1) through (3), (5), (9) through (11) are runs of present invention     Runs 4, 6 through 8 and 12 are comparative runs     CG: coil grinding      values outside scope of present invention.     *average value of 4 maximum depths among maximum depths of 20 examined     visual fields of surfaces of pickled sheet.     **largediameter roll → 4stand tandem mill, mediumdiameter and     smalldiameter rolls reverse mill.     ***6 months' exposure test to factory atmosphere.     ∘: good     Δ: poor     x: bad

Industrial Applicability

According to the present invention, stainless steel strip and sheetshaving superior surface properties can be provided by a process in whichthe coil grinding step, which is indispensable for obtaining stainlesssteel sheets, especially a product having a superior surface gloss, inthe conventional technique, is omitted, and a tandem mill havinglarge-diameter work rolls, which has a high productivity, is effectivelyutilized instead of a Senzimer mill having small-diameter work rolls.

The present invention provides excellent effects of reducing themanufacturing cost, increasing the productivity, and shortening theproduction time in the production of stainless steel sheets.

What is claimed is:
 1. A process for production of stainless steel thinstrip and sheets having a superior surface gloss and high rustingresistance, which comprises heating a continuously cast slab orpartially processed slab of ferritic or martensitic stainless steelcontaining 10 to 35% by weight of Cr at a temperature of 1100° to 1300°C. in a combustion atmosphere having an oxygen concentration lower than7% while adjusting the staying time of from preheating to extraction tofrom said atmosphere to less than about 260 minutes, carrying out hotrolling while maintaining the rolling-finish temperature at a levelhigher than 900° C., winding the hot rolled strip at a temperaturehigher than 600° C., carrying out mechanical descaling by adding agrinding and descaling agent having a maximum particle size smaller than400 μm to high-pressure water and spraying the mixture onto the steelstrip, pickling the steel strip, cold-rolling the steel strip whilemaintaining the relationship between the roll diameter and the reductionratio within the "overlap"-free region shown in FIG. 3, and subjectingthe steel strip to final annealing.
 2. A process for the production ofstainless steel thin strip and sheets having a superior surface glossand high resulting resistance, which comprises heating a continuouslycast slab or partially processed slab of frerritic or martensiticstainless steel containing 10 to 35% by weight of Cr at a temperature1100° to 1300° C. in a combustion atmosphere having an oxygenconcentration lower than 7% while adjusting the staying time of frompreheating to extraction to from said atmosphere to less than about 260minutes, carrying out hot rolling while maintaining the rolling-finishtemperature at a level higher than 900° C., carrying out mechanicaldescaling by adding a grinding and descaling agent having a maximumparticle size smaller than 400 μm to high-pressure water and sprayingthe mixture onto the steel strip, prickling the steel strip,cold-rolling the steel strip while maintaining the relationship betweenthe roll diameter and the reduction ratio within the "overlap"-freeregion shown in FIG. 3, and subjecting the steel strip to finalannealing by carrying out final annealing in a combustion gasatmosphere, and then pickling he final annealed strip.
 3. A processaccording to claim 1 or 2, wherein the steel strip is subjected todescaling using high-pressure water at an intermediate stage of the hotrolling step.
 4. A process according to claim 1 or 2, wherein whilemaintaining the relationship between the roll diameter and the reductionratio within the "overlap"-free range shown in FIG. 3, cold rolling isfirst carried out by using work rolls having a diameter of at least 150mm and then finish cold rolling is carried out by using work rollshaving a diameter smaller tan 100 mm.
 5. A process according o claim 2,wherein the final annealing is a bright annealing.
 6. A processaccording to claim 1 or 2, wherein the grinding and descaling agent isiron sand.
 7. A process according to claim 2 wherein after the hotrolling, aid process further comprises the step of winding thehot-rolled steel strip at a temperature higher than 600° C.
 8. A processaccording to claim 1 comprising carrying out said final annealing in acombustion gas atmosphere, and further comprising pickling he finalannealed strip.